Species Description:Polydora ligni is an opportunistic polychaete in the family Spionidae (Zajac and Whitlatch 1982). Spionid polychaetes are among the most common invertebrates found in the coastal, estuarine, and marine benthic environments (Anger et al. 1986). In some areas this mudworm has been identified as the cause of extensive oyster mortality (Zajac 1991a).

II. HABITAT AND DISTRIBUTION

Regional Occurrence:Polydora ligni occurs along the east and west coasts of North America, Gulf of Mexico and Europe. The polydora mudworm occurs both subtidally and intertidally along both coasts of the United States in bottom sediments and on the surface utilizing various substrata (Orth 1971, Zajac 1991a).

IRL Distribution:Polydora ligni is common in the Indian River Lagoon.

III. LIFE HISTORY AND POPULATION BIOLOGY

Age, Size, Lifespan:
The average life span for the polydora mudworm is reported to be 13 months
with some individuals living up to 31 months (Anger et al. 1986).
Polydora ligni larvae settle in late spring (rarely in summer) and
can have a lifespan as short as 10 weeks after settlement (Zajac 1991b).
P. ligni grows rapidly reaching sexual maturity at approximately 37
days and forming egg capsule by the time they are 2 months old. The ratio
of males to females is approximately 1 to 2.5 in observed populations and
females typically grow significantly larger than males of the same age
(Zajac 1991a). Adults are small, approximately 1 inch long and 1/4 inch
wide.

Abundance:
The mud tubes formed by Polydora ligni have been known to be very
abundant at certain times of the year in temperate environments where
densities are highest in the late spring and early summer (Zajac and
Whitlatch 1982, Zajac 1991a). In the Chesapeake Bay, the polydora mudworm
is thought to be one of the most abundant polychaete worms. Studies report
an average of 66 tubes per square centimeter of surface (Orth 1971).
During reproductive seasons, the pelagic larvae of the polydora mudworm can
be dominant in coastal zooplankton communities (Anger et al. 1986).
Regions that are densely populated with P. ligni are considered to
be an indicator of organic pollution (Anger et al. 1986, Zajac 1991a).

Reproduction:
Individuals of the polydora mudworm are usually male or female although
there are cases where hermaphrodites have been reported for this species.
Polydora ligni spawn throughout the year usually with two major
spawning periods in the spring and fall. Gametes are produced in the
segments at the middle half of the body. These are termed the gametogenic
segments. During reproduction, the males will release spermatophores onto
the sediment surface and the females will use their palps to direct the
spermatophores into their tubes for storage in seminal receptacles.
Fertilization most likely occurs when the eggs are deposited in capsules.
P. ligni larvae are brooded in capsules attached together in a
beaded string in the tube of the female polychaete (Zajac 1991a). Each
brood can have over 2000 larvae with approximately 90 eggs per capsule
(Orth 1971). As soon as one reproductive process is complete, a female will
begin to produce another batch of eggs for fertilization and can produce a
maximum of 8 broods in a lifetime (Zajac 1991a, b).

Embryology:
The embryos develop into 3-setiger planktotrophic larvae within the
capsules before they are released. Under laboratory conditions this took
approximately 4 days. Larvae measure about 0.2 mm in length and have three
segments when they hatch. After reaching 0.3 mm in length, larvae grow a
fourth segment (Anger et al. 1986, Zajac 1991a). In field studies, larvae
of Polydora ligni were reported to be abundant in the plankton
during times coinciding with spawning periods from the spring to the fall
months (Orth 1971). In the laboratory, larvae were observed to settle and
metamorphose at 18 days when they reached a size of 15 segments.
Recruitment times differ regionally, but can occur throughout the year
(Zajac 1991a).

IV. PHYSICAL TOLERANCES

Temperature:
In laboratory experiments, the development of Polydora ligni larvae
was delayed when reared at < 10°C. At this temperature, individuals did not
settle until 60 days instead of 28 days observed for the individuals
reared at 20°C (Orth 1971, Anger et al. 1986).

Salinity:
There are no specific studies addressing the salinity tolerance of the polydora mudworm.

V. COMMUNITY ECOLOGY

Trophic Mode:Polydora ligni uses 2 grooved palps to capture surface sediments and particles suspended in the water column (Zajac 1991a). The fifth segment of the body has small hooks that anchor the worm to its tube while feeding.